石灰石の化学成分, 微顕鏡観察および熱分析

In the surroundings of Kochi City, there is limestone deposit of very good quality, and the amount of deposit that can be mined is estimated at about one billion and three hundred million tons. As the development of limestone mining in this area is progressing, the authors are conducting research for obtaining fundamental data about limestone as raw material of various industries, including especially the lime-manufacturing industry.<BR>Now, for the purpose of study, the mining region of limestone is divided into two areas, northern and southern districts of Kochi City, and samples were collected from various parts of ores reserved in each of these areas. By using these samples, the authors made determination of chemical composition, microscopic observation of fine structure of sliced samples and studies of thermal properties with thermal analysis. In addition mutual relation among results of these experiments was examined.<BR>1) Chemical composition : Analytical values of SiO₂, Fe₂O₃, Al₂O₃, CaO, MgO, MnO and P were obtained for about 160 kinds of samples. Generally, samples collected in northern area contained a small quantity of impurities and had homogeneous chemical compositon. Especially, purity of samples from kagami area was very high. Samples from southern area had generally much impurities.<BR>2) Microscopic observation : Slices made from samples were observed with parallel and crossed Nicol prisms of microscope. Thus, fine structure of crystals and the existence of fossils were examined.<BR>Main mineral-component is calcite mostly composed of heterogeneous aggregation of fine, medium and coarse grains mixed with white and stripped calcite-veins. This structure is owing to further carbonation of fine grains of limestone. However, samples from Kagami area were limestones consisting of fine grains and had different structure from that of samples of other mineral deposits. Also, samples of sea urchin, sponge and fusulina etc.<BR>It seemed that coloured impurities and black and opaque organic substances are rarely found.<BR>3) Thermal analysis : Using Honda's thermal balance and the apparatus of differential thermal analysis, the loss of weight by heating and endothermic curve at a heating rate of 5 °C/min were obtained. There was a tendency that the temperature of complete decomposition was low (875-900°C) for samples from northern area and high (900-950°C) for those from southern area. The degree of thermal decomposition measured by thermal analysis almost agreed with the results of microscopic observation. For example, samples from Kagami area had structure of very fine crystals and at the same time showed low decomposition-temperature. Further, thermal analysis was conducted about black limestones containing much silicic acid, and special samples of high degree of crystallization.